There are two standards for a high density optical disc that conducts recording and/or reproducing (hereinafter referred to as “recording/reproducing”) of information by using a violet semiconductor laser with a wavelength of 405 nm. The two standards include HD DVD (hereinafter referred to as HD) that conducts recording/reproducing of information by using an objective lens having NA 0.65 and Blu-ray Disc (hereinafter referred to as BD) that conducts recording/reproducing of information by using an objective lens having NA 0.85. On the HD, it is possible to record information of 15 GB per one layer. On the BD, it is possible to record information of 25 GB per one layer. Hereafter, the optical disc of this kind is called “high density disc” in the present specification.
In an ordinary optical pickup apparatus such as one shown in Japanese Patent Publication open to Public Inspection No. 2002-082280, a light flux emitted from a semiconductor laser is changed in terms of an angle of divergence properly through a coupling lens (including a collimating lens), to enter an objective lens.